Production of phthalocyanine pigments



United rates ldatent @ftice 3,5l,72 Patented Aug. 28, 1962 3,651,720PRGDUCTTQN F PHEHALGQYANlNE PlGli EENTS John W. Minnich, Wilmington,Deh, assignor to E. l. the Pont de Nemours and Company, Wilmington, Deh,a corporation of Delaware N0 Drawing. Filed Dec. 29, 1958, 82;. to.783,1tl4 Claims. ('Cl. 26ti314.5}

This invention relates to a new process for obtaining phthalocyaninepigments in small particle size.

Phthalocyanine pigments are a well known class of coloring compounds.The copper phthalocyanines, particularly, find Widespread use in theblueto-green color range. These products have usually been prepared ineither of two ways. In one method, the phthalocyanine is produced byreacting phthalonitrile with a metal salt, usually a copper chloride.This reaction may be carried out in a melt system without any diluent,or it may be carried out With the raw materials in suspension in aninert high boiling solvent such as kerosene or trichlorbenzene. in thesecond route, which also may be carried out in a melt or in suspensionin inert solvents, phthalocyanine is produced by reacting phthalicanhydride With urea and a metal salt, such as a copper chloride.

One of the most widely used of the copper phthalocyanines isunsubstituted copper phthalocyanine which is a brilliant blue pigment.There are also available commercially substituted copper phthalocyanineswherein the substituents alter the properties and the hue of the pigmentin a desired manner. For instance, a small amount of chlorine, usuallyintroduced by adding a small amount of a suitably chlorinated phthalicanhydride derivative, confers crystal stability in certain organicsolvents which tend to cause a change in crystal phase. Introduction ofa small amount of a sulfonic acid group in the same general mannerconfers resistance to flocculation in coating composition vehicles.Substantially complete chlorination results in a brilliant greenpigment.

The phthalocyanine products obtained from these well known methods ofmanufacture usually require substantial particle size reduction beforeacceptable pigmentary properties are attained. Various methods ofreducing the particle size have been proposed and used in commercialoperations. One of the first methods to be described in the art is knownas acid pasting. in this method pigment is dissolved in a relativelylarge amount of concentrated sulfuric acid (or chiorsulfonic acid in thecase of the polychloro phthalocyanine compounds), and then it isprecipitated from this solution by rapid dilution with water. This is aneffective method of particle size reduction, yet it has certaindisadvantages. The use or" a large amount of these very strong acidsraises production costs, and there are problems involved in handlingsuch large quantities of acid and water. Also, it has been the commonexperience of those who have used this method of particle size reductionthat the products require special treatment during the drying operationin order to avoid agglomeration and a consequent loss of much of theadvantage obtained by the acid pasting operation.

A modification of the acid pasting method, known .as acid swelling, hasalso been used. In an acid swelling operation, concentration of the acidand the amount thereof are adjusted so that the pigment is not actuallydissolved in the acid but appears to be affected by a sort of swellingof the crystals. It is possible that there is some formation of asulfate of a phthalocyanine in this operation, but there is notsuflicient acid nor a sufiicient concentration of the acid to actuallyresult in true solution. Nevertheless, on dilution of this mixture withwater, the phthalocyanine is regenerated in its original chemical formin a smaller particle size than the original.

Such a method is described in FIAT Report 1313 (P845172), vol. 111,pages v298-303 and 442448. According to this report, up to as much as 20parts of acid per part of pigment are used, and the concentration of theacid is in the range or" 6080%. The process also requires a temperatureof BIS-40 C. and vig r us gi ation for 14-20 hours. Experience has shownthat this method, although reasonably successful, falls considerablyshort of modern quality standards in most cases. Moreover, the largeamount of acid and the very long time required are undesirable featuresof this process.

The present invention concerns a process which preconditionsphthalocyanine pigments prior to acid swelling. This preconditioningcomprises dry milling the pigment in the absence of any milling aid in amilling apparatus having an attrition and shearing action. Because ofthis preconditioning, the ultimate product from the acid-swellingoperation is found to possess far superior pigment properties. Theresults obtained by this preconditioning operation are quite surprisingsince in the past attempts to reduce the particle size of pigments bydry grinding in the absence of added agents have been without success.Moreover, such dry grinding failed to show any beneficial effect uponthe pigment, and in some instan es appeared to be detrimental.

F or instance, when a crude copper phthalocyanine pigment is ground inthe dry state in the absence of any added inert substance such as sodiumchloride or borax, there is no evidence of any substantial reduction inparticle size when examined by any of the tests usually applied to suchpigments. There is no increase in tinctorial strength; rather, it iscommon to observe a marked decrease in strength. There is no improvementin intensity of color, nor is there any evidence of significantlysmaller particle size by either microscopic observation or surface areameasurements. These tendencies are particularly serious when thegrinding is done in a ball mill; and it has even been observed that asmall particle size copper phthalocyanine finished by other methods willrevert largely to the properties of a crude pigment when subjected to drgrinding in a ball mill. The effect is not limited to ball millgrinding; it is observed to a lesser degree in other dry grindingmethods, such as may be found in a hammer mill or even in a mortar andpestle. in short, all prior experience has led to the presumption thatdry grinding is not an etfective method for particle size reduction ofphthalocyanine pigments.

In the process of this invention for the comminution of crudephthalocyanine pigments, the first step of dry milling in the absence ofany milling aid is preferably carried out in ball mill. The milling isfollowed by the acid swelling operation and then the pigment and acidare drowned in water to regenerate the phthalocyanine in small particlesize, and this product is recovered by conventional means. In apreferred embodiment of this invention, a phthalocyanine is dry groundfor about 6 hours in a conventional manner in a ball mill in the absenceof any grinding aid. After the discharge of the dry pigment from themill, it is slurried in 34 parts of sulfuric acid of about 65-85%concentration, and after complete wetting, it is allowed to stand incontact with the acid for about one hour at about room temperature, e.g.in the range of 1030 C. The slurry is then rapidly diluted with arelatively large amount of water, heated for a short time near theboiling point, and then filtered, washed free of soluble salts and driedin a conventional manner to give a pigment of superior tinctorialproperties.

This preferred process can be used with any of the various forms ofphthalocyanine. However, in the case of the polychloro phthalocyaninederivatives, the preferred acid concentration is increased to the rangeof 93-100% sulfuric acid.

J For a clearer understanding of the invention, the following specificexamples are given. These examples are intended to be merelyillustrative of the invention and not in limitation thereof. Unlessotherwise specified all parts are'by weight.

Example I 18 parts of a substantially chlorine-free copperphthalocyanine pigment (obtained by the reaction at an elevatedtemperature of phthalic anhydride with urea and copper chloride inkerosene and in the presence of ammonium molybdate as a catalyst) ischarged to a ball mill containing about 1000 parts of Cyl-pebs (Cyl-pebsare steel rods approximately 42" x 1"). The size of the mill is suchthat the full charge of pigment and Cyl-pebs occupies approximately 6065of the total volume of the mill. The mill is rotated at about 70% of thecritical speed (the critical speed is that at which the centrifugalforce overcomes the force of gravity so that the grinding elements areretained against the outer wall of the mill) for about 6 hours. The drypowder is discharged from the mill through a suitable screen. l5parts ofthis dry powder is then mixed with 55 parts of 70% sulfuric acid usingonly. suflicient agitation to completely wet the dry powder. Some heatis developed during this operation, but no added heat is necessary noris any cooling necessary under normal circumstances. The mixture of acidand pigment is allowed to stand for about 1 hour after which 300 partsof cold water is added. Agitation is then commenced and the slurry isheated to the boil and stirred for about /2 hour at the boil. It is thenfiltered, washed free ofsoluble salts and the pigment is dried at 80 C.to give a red shade copper phthalocyanine pigment of superior tinctorialstrength.

Example I] In this example the process is applied to a copperphthalocyanine pigment containing about 4.5% chlorine (obtained by thereaction at an elevated temperature of a suitable mixture of 4-chlorphthalic acid and phthalic anhyclride with urea and copper chloride inkerosene and in the presence of ammonium molybdate as a catalyst). The.milling operation for this chlorine-containing copper phthalocyanine isthe same as that shown in the first part of Example I, except that it iscarried out for only 4 hours instead of 6 hours. 15 parts of theresulting dry powder is then mixed with 40 parts of 80% sulfuric acidand the mixture is allowed to stand for 1 hour, after which 1000 partsof water is added. Agitation is then commenced and the slurry is heatedto the boil, boiled for about /2 hour and the pigment isolated byfiltering. It is then washed free of soluble salts and dried at 80 C. togive a pigment possessing good tinctorial strength, excellent intensity,and the characteristic crystal stability of such chlorine-containingproducts.

Example III The pigment of this example is a flocculation resistantcopper phthalocyanine containing both chlorine and sulfonic acid groups.It is made substantially as described in U.S. 2,799,594 by reacting atan elevated temperature a suitable mixture of 4-sulfophthalic acid,4chlorophthalic acid and phthalicanhydride with urea and copper chloridein kerosene and in the presence of ammonium molybdate as a catalyst.The. millingoperation is carried out asdescribed in Example I exceptthat it is continued forabout 18 hours. 25 parts of the resulting drypowder is mixed with 90 partsof 80% sulfuric acid and allowed tostand-for 1 hour and then diluted with 1000 parts of water. Agitationisthencommenced and the slurry is heated to the boilland stirred about Ahour at the boil. The pigment is recovered from the slurry, washedsubstantially free. of :soluble. salts, and dried at about 80 C. to:givea crystal-stable, flocculation-resistant pigment of goodtinctorialstrength. If desired, the filter cake from the acid swelling step may beconverted to a rosinated lake plete chlorination.) to a ball millcontaining about 1000 parts of Cyl-pebs.

by conventional techniques. This practice is sometimes followed withphthalocyanines containing sulfonic acid groups since this overcomes thetendency for the pigment to'become hard upon drying. The lakes usuallycontain 3040% rosinate and 60-70% phthalocyanine pigment.

Example IV The size of the mill is such that the full charge of pigmentand Cyl-pebs occupies approximately 60-65% of the total volume of themill. The mill is rotated at about 70% of the critical speed for about 5hours. 25 parts of the resulting dry powder is then mixed with 100 partsof sulfuric acid of 95 .5 concentration. After standing for about 1 hourat room temperature, 1000 parts of water is added to the mixture.Agitation is then commenced and the mixture is heated to the boil andheld at this temperature for about Z2 hour while stirring. The pigmentis then isolated by filtering, washed substantially free of solublesalts, and dried at about C. to give a brilliant green pigment of goodtinctorial strength and intensity.

Example V A 1000 gal. ball mill, approximating 6 in length by 6' indiameter, is charged with approximately 24,000 lbs. of /a" x 1" Cyl-pebstogether with about 3000 lbs. of common railroad'spikes (these areintroduced to prevent any caking in the mill). 1200 lbs. of achlorine-free copper phthalocyanine substantially identical with thatused in Example I is then added to the mill and it is operated at about70% of critical speed for about 6 hrs. after which the dry powder isdischarged from the mill through a suitable screen to retain thegrinding elements in the mill.

50 parts of water is then added to a separate container arranged'forsimple agitation and 138 parts of 96% sulfuric acid is added theretowith careful agitation to give approximately 70% concentration of H SOin the solution which is then cooled to below 30 C. At this point, 50parts of the dry powder from the milling operation above is added to theacid solution and the agitation is continued until the dry powder is allwet after which the agitation is discontinued and the mixture is allowedto stand without agitation for about 1 hr. 1000 parts of water is thenadded rapidly. The agitation is then started, and the mixture is heatedto the boil and held there for about /2 hr. with the agitator stillrunning. The slurry is then filtered, washed substantially free ofsoluble salts and substantially free of acid and finally dried at 80 C.to give a red shade copper phthalocyanine pigment of superior tinctorialproperties.

In the examples above, the process of this invention has been shown tohave utility in the particle size reduction of various copperphthalocyanine pigments including copper phthalocyanine per se, thepartially chlorinated and the substantially chon'nated species, and alsocopper phthalocyanine containing other substituents such as the sulfonicacid group. The process of this invention is also applicable to theparticle size reduction of metal-free phthalocyanine and metalphthalocyanines other than copper phthalocyanine. For example, nickel.phthalocyanine, cobalt phthalocyanine, aluminum phthalocyanine, ironphthalocyanine and also the corresponding partially chlorinated orsubstantially chlorinated derivatives can be reduced in particle size.Likewise, it is applicable to mixtures of these products, especially tomixtures of copper phthalocyanine with other metal phthalocyanines andwith various substituted phthalocyanines, such as halogenatedandsulfonated species.

It is well known in the art that unsubstituted copper phthalocyanine iscapable of existing in two crystal phasesone of these phases is areddish shade of blue, while the other is a greenish shade of blue.Although there is some confusion in the pigment art as to thedesignation of these two crystal phases, the most widely acceptednomenclature refers to the phase possessing the reddish shade as thealpha crystal phase (see FIAT Report 1313, vol. 111) and the phasepossessing the greenish shade as the beta crystal phase (see US. Patent2,556,726). When the present invention is applied to unsubstituted CPC,the ultimate product will always be the reddish shade product which isin the alpha crystal phase.

The conditions applicable to the dry milling operation which is thefirst step in this process are not especially critical. The mill loadingis substantially conventional for ball milling operations. Thus, it isconventional for the charge of grinding media to occupy something lessthan /2 of the volume of the mill and for the material being ground tooccupy considerably more than the voids between these media so that thetotal charge in the mill is in the range of 6065% of the total volume ofthe mill. It is quite possible to increase the charge to the range ofabout 75% of the volume of the mill with some increase in the millingtime. The choice of these conditions is well within the skill of oneversed in this type of operation. The preferred grinding media in themills are the rod type Cyl-pebs described above in Example I, and thesemay vary in size. It is also possible to use ordinary round steel ballsvarying from /8" in diameter up to /2" in diameter or more. When roundballs are used, there is a tendency for the charge to cake in the millunder some conditions. Such caking is often avoided by the use of someirregularly shaped grinding media, such as nails. The use of the rodtype Cyl-pebs usually obviates this difficulty. As already pointed out,the optimum time of grinding will vary somewhat with the mill loadingand, also to some degree with the type of pigment being milled. Aminimum of 4-6 hours is usually required and this may be extended to asmuch as 12-18 hours. It is characteristic of this operation and one ofthe unexpected features that the dry powder obtained following themilling step shows no significant improvement with respect to ordinarypigment properties over the original crude pigment. It is only When thesubsequent acid swelling step is applied to this powder that itsimproved properties become apparent.

Although the preferred method of dry milling is in a ball mill, any typeof milling or grinding apparatus in which the grinding action is due toattrition or shearing action as distinguished from impact action may beused. Grinding apparatus having an impact action, such as a pulverizeror micronizer, produce inferior results. On the other hand, rod mills aswell as stirred and vibratory types of bail mills in contrast to theusual rotating type are additional examples of grinding equipment havingan attrition or shearing action on the pigment.

In the acid swelling step of this invention, there are certain broadlimits which are applicable with preferred ranges of special value.Thus, the concentration of the sulfuric acid may range from about 50% toabout 100%. Within this range 65-85% concentration is preferred for thecopper phthalocyanine blue pigments and about 93-95% for the polychloroderivatives. Therefore, the preferred acid concentration range whichincludes both the copper phthalocyanine blue pigments and the polychloroderivatives is 65 %95%. Within the broader range excellent products areobtained, but the preferred ranges give the optimum products.

The amount of acid may vary from about 2 parts per part of pigment up toabout 12 parts per part of pigment, these figures being based upon thetotal amount of acid solution used regardless of its concentration.Within this range, 3-4 parts of acid per part of pigment give entirelysatisfactory results and are preferred for reasons of economy over thelarger amounts.

With respect to the temperature during the acid swelling step, it iscommon to start with the acid at a temperature of 10 C.30 C. Heating upto as much as 50 C.-6() C. or cooling below 10 C. would do no harm tothe process but does not oifer any advantage and consequently is not apreferred step.

The degree of agitation required for the acid swelling step is one pointof clear distinction over the prior art which has suggested a similaroperation requiring a shearing action. It is found in this process thatthe only agitation required is that necessary to completely wet thepigment with the liquid. It is usual to continue the agitation only solong as required to wet the pigment and then to allow the material todigest simply by standing for a time in the range of about 1 hour.However, the digestion time may be considerably less, e.g. as little as5 minutes, and it may extend to a much longer period such as 24 hourswithout any significant variation in the final results.

The regeneration of the pigment by dilution with water is entirelyconventional and the only requirement is that there is sufficient waterto hydrolyze any phthalocyanine sulfate formed as a result of contactingthe pigment with the sulfuric acid. Usually, dilution to an acidconcentration of 10-30% is suflicient to accomplish this, but it mayvary outside these limits depending upon the particular conditions beingused. It is common to heat the diluted mixture to the boil to promotehydrolysis and to improve the efficiency of the acid extraction step.Although preferred, it is not an essential step in the new process.

The two-step process of this invention Offers a significant advantageover the one-step acid swelling operations of the prior art since itproduces products of markedly superior tinctorial properties withoutusing special equipment or large amounts of acid. The process of thisinvention is especially advantageous for the preparation of a red shade,chlorine-free copper phthalocyanine as shown in Example 1. Such productshave outstanding tinctorial properties and the process shows substantialeconomic advantages as compared with other means for producing productsof similar tinctorial properties.

Since it is obvious that many changes and modifications can be made inthe above-described details without departing from the nature and spiritof the invention, it is to be understood that the invention is not to belimited to said details except as set forth in the appended claims.

I claim:

1. A process for the comminution of a phthalocyanine pigment whichcomprises dry milling said pigment in a milling apparatus having anattrition and shearing action, subsequently acid swelling saiddry-milled pigment, and recovering a finished phthalocyanine pigmentproduct.

2. A process according to claim 1 in which said dry milling step isconducted in a ball mill.

3. A process for the comminution of a phthalocyanine pigment whichcomprises dry milling said pigment in a ball mill, contacting Saiddry-milled pigment with from 2-12 parts of sulfuric acid per part ofpigment, said sulfuric acid having a concentration of from 50-100%,adding suflicient water to hydrolyze the copper phthalocyanine sulfateformed as a result of contact with the H and recovering the finishedphthalocyanine pigment product.

4. A process according to claim 3 in which there are 3-4 parts ofsulfuric acid per part of pigment and the concentration of the acid isfrom 65-95%.

5. A process for the comminution of a phthalocyanine pigment selectedfrom the group consisting of the substituted and unsubstituted copperphthalocyanines, nickel phthalocyanines, cobalt phthalocyanines,aluminum phthalocyanines, iron phthalocyanines, and mixtures thereof,which comprises dry milling said pigment in a ball mill, contacting saiddry-milled pigment with from 2-12 parts 9 7 of sulfuric acid per part ofpigment: said sulfuric acid having a concentration of from 50-100%,adding sufiicient water to hydrolyze the copper phthalocyanine sulfateformed as a result of contact with the H 80 and recovering the finishedphthalocyanine pigment product.

6. The process of claim 5 in which the phthalocyanine is chlorine-freecopper phthalocyanine.

7. The process of claim 6 in which there are 3-4 parts of sulfuric acidper part of pigment and the concentration of the acid is from 65-85%.

8 The process of claim 5 in which the phthalocyanine is copperphthalocyanine analyzing about 4.5% chlorine and the concentration ofthe sulfuric acid is about 80%.

9. The process of claim 5 in which the phthalocyanine is copperphthalocyanine substituted with chlorine and 8 sulfonic acid groups andthe concentration of the sulfuric acid is about 80%.

10. The process of claim 5 in which the phthalocyanine is polychlorocopper phthalocyanine analyzing about 14.5 atoms of chlorine permolecule and the concentration of the sulfuric acid is about 95%.

References Cited in the file of this patent UNITED STATES PATENTS2,284,685 Detrick et a1. June 2, 1 942 2,716,649 Brouillard Aug. 30,1955 2,770,629 Eastes Nov. 13, 1956 2,857,400 Cooper Oct. 21, 1958FOREIGN PATENTS 503,666 Great Britain Apr. 12, 1939

3. A PROCESS FOR THE COMMINUTION OF A PHTHALOCYANINE PIGMENT WHICHCOMPRISES DRY MILLING SAID PIGMENT IN A BALL MILL, CONTACTING SAIDDRY-MILLED PIGMENT WITH FROM 2-12 PARTS OF SULFURIC ACID PER PART OFPIGMENT, SAID SULFURIC ACID HAVING A CONCENTRATION OF FROM 50-100%,ADDING SUFFICIENT WATER TO HYDROLYZE THE COPPER PHTHALOCYANINE SULFATEFORMED AS A RESULT OF CONTACT WITH THE H2SO4, AND COVERING THE FINISHEDPHTHALOCYANINE PIGMENT PRODUCT.